Apparatus and method for dynamically adjusting an electric arc furnace

Abstract

An apparatus for regulating an electric arc furnace connected to a power supply system with at least one system phase that applies an AC voltage to a furnace electrode and an arc current for melting. A control loop device includes an electrical converter designed for negative feedback of an amplitude and/or frequency of the AC voltage to produce an amplitude and/or frequency of the arc current. The converter includes an input port having a system power supply connected thereto, and an output port having a melting furnace power supply and a primary circuit of a first transformer connected thereto, wherein a secondary circuit of the first transformer is connected to the arc furnace electrode. A primary coil of a second transformer is connected in parallel with the converter input port, and a secondary coil of the first transformer is connected in series with a secondary coil of the second transformer.

The invention claimed is: 
     
       1. An electric arc furnace comprising:
 a power supply system with at least one system phase for applying an alternating electrical voltage and an arc current; 
 a furnace electrode fed by the power supply system; 
 a control loop device comprising an electrical converter configured for reverse feedback of an amplitude and/or a frequency of the alternating voltage to an amplitude and/or a frequency of the arc current, wherein the electrical converter comprises a two-port network comprising an input port and an output port; 
 the power supply system attached to the input port; 
 a melting furnace power supply connected to the output port; 
 a primary circuit of a first transformer electrically connected to the output port; 
 a secondary circuit of the first transformer electrically connected to the furnace electrode; 
 a primary coil of a second transformer electrically connected in parallel to the input port of the electrical converter; and 
 a secondary coil of the second transformer electrically connected in series with a secondary coil of the first transformer. 
 
     
     
       2. The furnace of  claim 1 , wherein a ratio of a primary electric rated power of the first transformer to one of the second transformer is adjustable. 
     
     
       3. The furnace of  claim 1 , wherein a ratio of the primary electric rated power of the first transformer to that of the second transformer is 1:3. 
     
     
       4. The furnace of  claim 1 , wherein the first transformer is a step-up or boost transformer. 
     
     
       5. The furnace of  claim 1 , wherein the first transformer is removed, and the output port of the converter is electrically connected in series with the secondary coil of the second transformer and to the furnace electrode. 
     
     
       6. The furnace of  claim 1 , wherein the electrical converter adjusts the amplitude and/or the frequency of the alternating electrical voltage as the manipulated variable for controlling the amplitude and/or frequency of the arc current as the controlled variable. 
     
     
       7. The furnace of  claim 1 , wherein the electrical converter adjusts the amplitude and/or the frequency of the arc current as the manipulated variable for controlling the amplitude and/or frequency of the alternating electrical voltage as the controlled variable. 
     
     
       8. The furnace of  claim 1 , wherein the electrical converter increases the amplitude and/or the frequency of the alternating voltage when the amplitude and/or the frequency of the arc current is decreased, and decreases the amplitude and/or the frequency of the alternating voltage when the amplitude and/or the frequency of the arc current is increased. 
     
     
       9. The furnace of  claim 4 , wherein the electrical converter decreases the amplitude and/or the frequency of the arc current when the amplitude and/or frequency of the alternating voltage increases, and increases the amplitude and/or the frequency of the arc current when the amplitude and/or frequency of the alternating voltage decreases. 
     
     
       10. The furnace of  claim 1 , wherein the electrical converter converts an alternating magnitude of the power supply system into an alternating magnitude of the furnace electrode with phase synchronicity. 
     
     
       11. The furnace of  claim 1 , wherein the electrical converter is configured for electrical connection to any desired voltage level of the electrical power supply system. 
     
     
       12. The furnace of  claim 1 , wherein the electric arc furnace comprises three graphite furnace electrodes supplied with power by three system phases, wherein amplitudes and/or frequencies are controllable by three converters. 
     
     
       13. The furnace of  claim 12  wherein amplitudes and/or frequencies are separately controllable by the three converters.